Use SP Flash tool from the ZIP.
Go to Download tab.
Choose Download agent - DA_SWSEC.bin from SP Flash folder.
Choose Scatter - MT6795_Android_scatter.txt from images folder
And finally and very important - UNCHECK preloader (if don't - you are going to brick RMN3)
Then flash as usual with SP Flash:
Select Download Only option.
Press Download button.
Turn off RMN3.
Press only vol down button on RMN3 and plug USB cable immediately. Keep button pressed.
See the red bar in SP Flash. Now you can leave the button.
See the yellow bar in SP Flash - that means flashing is started, wait until progress is 100% and window with green check mark appear. Flashing is done.
Now disconnect USB cable, close the SP Flash and turn on RMN3. First start may take up to 10 minutes.

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Thanks to Xiaomi.eu for the Rom

Here is a link for xiaomi.eu 7.1.6.0 Stable Multi ROM Rooted and Mod by LoXaR for SP Flash Tool - Reply to Download

@LoXaR should i wait for the new 6.1.X ROM get out later this week or flash this 7.1.X ROM ? I'm already on 6.1.21 .
What's the difference between both ? I know one is a dev release and the other is a (stable) one but wich one is better for daily use and battery life friendly ?? Thx for anyone who help me :)